1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus such as a laser printer and a duplicator. More particularly, aspects of the present invention relate to a guide apparatus for mounting and dismounting an inner part such as a paper counter-transfer guiding part of a duplexed printing unit with respect to a frame of a device body and an image forming device having the same.
2. Description of the Related Art
Generally, a duplex printing image forming apparatus, for example, a duplex printing laser printer 1, as illustrated in FIG. 1, includes a duplex printing unit 80 that re-inserts paper P, having one side already printed, into a developing unit 30 and a fixing unit 40 to have the paper P printed on the other side.
The duplex printing unit 80 includes a paper counter-transfer guiding part 62. The paper counter-transfer guiding part 62 is a part of a paper returning path B that allows the paper P having one side already printed to advance into the developing unit 30 and have the other side printed. A paper transfer direction switching part 54 switches the paper transfer direction when the paper P is move to the paper returning path B in a duplex printing operation.
The paper counter-transfer guiding part 62 includes first and second counter-transfer rollers 70, 90 to move the paper P through the paper returning path B. The paper counter-transfer guiding part 62 is formed to be mountable and dismountable with respect to a frame 14 (FIG. 2) inside a printer body 10 to allow for a removal of a paper jam. As such, the paper counter-transfer guiding part 62 is formed in a square housing, and the frame 14 of the printer body 10 has a first and a second guide rails 95 (the first guide rail being shown) formed in first inner and second inner side surfaces 16 (the first guide surface being shown) of the printer body 10 to guide respective lower parts of both sides of the paper counter-transfer guiding part 62.
The paper transmitting direction switching part 54 is arranged at the point where the paper transfer path A encounters the paper counter-transfer path B upstream of a discharge roller 60 of a discharge unit 50. In duplex printing operations, the paper transmitting direction switching part 54 rotates toward the position indicated in a solid line of FIG. 1 so as to guide the paper P, having one side printed, toward the paper counter-transfer path B in preparation of the paper P reentering the developing unit 30.
The conventional laser printer 1, constructed as is described above, includes the first and second guide rails 95 formed in the first and second side walls 16 as separate structures. The first and second guiding rails guide the paper counter-transfer guiding part 62 to be mountable and dismountable with respect to the frame 14 of the printer body 10, to allow for the removal of paper jams. That is, as illustrated in FIG. 3, a structure 16′, such as the H-shaped frame 14, shown in FIG. 2, may not be separated from inner metallic patterns 97 after they are molded together, due to a protrusion 95′, such as the guide rail 95, existing therein. That is, the structure 16′ is designed to undercut the protrusion 95′. Accordingly, the inner protrusion 95′, such as the guide rail 95, may not be integrally formed with the structure 16′, but must be mounted therein as a separate part after the structure 16′ is manufactured.
When the first and second guide rails 95 are mounted in the frame 14 as separate parts, one is required to separately mount the first and the second guide rails 95 in the first inner and second inner side surfaces 16 of the frame 14 by use of a fixing device such as a screw. Accordingly, manufacturing time and numbers of processes are increased, which leads to productivity deterioration and increases in manufacturing costs.
Also, when the first and second guide rails 95 are not precisely mounted in the frame 14 due to manufacturing errors of the fixing device, the paper counter-transfer guiding part 62, which is mounted along the first and the second guide rails 95, may not be precisely located. As such, the paper P, being counter-transmitted by the paper counter-transfer guiding part 62 in duplex printing operations, may suffer paper jams.
In addition, since the first and second guide rails 95 are mounted in the first and second side walls 16 of the frame 14 by the fixing device, a fixing part, such as a screw hole, must be made. Accordingly, a crack caused by manufacturing faults in the fixing part may be worsened by repeated mounting and dismounting operations of the paper counter-transfer guiding part 62 with respect to the. Also, the fixing parts may be damaged by shocks and as a result, escape from the first and the second side walls 16 or be forced away from the proper positions thereof, which may lead to malfunctions.